Materials testing grip



Filed May 2l, 1965 R. c. CAVANAUGH ET AL 3,375,710

MATERIALS TESTING GRIP L 2 Sheets-Sheet l April 2, 1968 R. c. CVANAUGH ET'AL 3,375,710

MATERIALS TESTING GRIP United States Patent Oiice j 3,375,710 Patented Apr. 2, 1968 3,375,710 MATERIALS TESTING GRIP Ronald C. Cavanaugh, Holbrook, and Donald C. Holmes,

North Weymouth, Mass., assgnors to Instrou Corporation, Canton, Mass., a corporation of Massachusetts Filed May 21, 1965, Ser. No. 457,715 11 Claims. (Cl. 73-103) This invention relates to fluid operated grip apparatus for materials testing and more particularly to the control of high pressure clamping jaws in such apparatus.

It is a primary object of the invention to provide high pressure grip apparatus in which the article to be clamped can be safely secured in the desired clamping position prior to the application of high pressure.

Generally speaking, the invention features grip apparatus in which a movable jaw can be ybiased at low pressure in its clamping position, thereby securing the clamped article, after which a high pressure uid line is actuated. In preferred embodiments, there is featured a double piston arrangement in which one piston moves the jaw to its clamping position and the other piston transmits the high pressure, as well as control circuitry that prevents the application of high pressure until the low pressure piston has been actuated.

Other objects, features, and advantages will appear from the following description of a preferred embodiment of the invention, taken together with the attached drawings thereof, in which:

FIG. 1 is a partially sectioned elevation and FIG. 2 is a schematic diagram of the grip apparatus.

Referring now more particularly to the drawings, there is shown in FIG. l a grip having a generally D- shaped frame 12 of generaliyirectangular cross section. Shank 13 is provided at the top of the frame for installation of the grip into associated machinery. Opposing frame portions 14, 16 support the two clamping jaws 18, 20, and in addition house mechanism for controlling the jaws.

Adjustable stationary jaw 20' is mounted on a short shaft 22 disposed in a vertical slot in jaw holder 24 and retained therein by horizontal (in FIG. 1) pin 26. Jaw holder 24 is in turn disposed in cylindrical bore 28 in frame portion 16. Dowel 30 passes through the wall of the frame into horizontal slot 32 in holder 24, preventing rotation of the holder. Adjusting screw 34 is threaded at one end into bore 36 in the right hand end of holder 24. The other end of screw 34 is unthreaded and passes through frame end cap 38, terminating at knurled adjustment knob 40.

`Movable jaw 18 is mounted on shaft 42 disposed in low pressure piston jaw actuator 44 and retained therein by vertical pin 46. Pins 26 and 46 are oriented with their axes perpendicularly related, giving jaws 18 and 20 a slight amount of rotational freedom about vertical and horizontal axes respectively, which enables them to seat firmly against the clamped object.

Frame portion 14 has a stepped cylindrical bore 48,` closed at its left hand end -by pressure cap 50 secured to the frame by machine screws (not shown). O-ring 52 seals between the frame and cap 50. Cap 50 has a recess 54 forming a continuation of the left end of bore 48. Passage 56 through cap 50 enables the introduction of oil at high pressure into recess 54.

of one grip;

Piston jaw actuator 44 is disposed in the reduced diameter right hand portion of bore 48, though it extends leftwardly of shoulder 49 into the larger portion of the bore. Dowel 60 extends into slot 62 in piston 44 to restrain rotation of the piston. Quad ring 63 seals between the piston and bore 48.

The left hand portion of piston 44 consists of an outer annular spindle portion 64, terminating in ange 66, and an inner shank portion 68 spaced from portion 64 and extending to the left substantially beyond flange `66. Quad ring 70 seals between ange 66 and bore 48.` When piston 44 is in its leftwardmost position flange 66- is spaced from shoulder 49, providing an -air pressure chamber 72 to the right of iiange 66. Passage 74 through the wall of frame portion 14 enables the introduction of pressurized air into chamber 72.

Coil spring 78 is located in the annular space between spindle 64 and shank 68, and is of sucient uncompressed length to extend leftwardly around shank 68 beyond liange 66.

High pressure piston jaw actuator 80 is shaped at its left end to seat in recess 54 of pressure cap 50. Flange 82 at the right end of piston 80 is of the same diameter as flange 66 and abuts shoulder 51 of pressure cap 50 wheny the piston is fully seated in recess 54. O-ring 8'6 and back-up ring 87 to the left of rin-g 86, seal 'between iiange 82 and bore 48. The free left end of shank 68 iits into axial bore 84 in piston 80, compressingspring 78 in its leftwardmost position. The diameter of bore 8-4 is smaller than the inside diameter of spindle 64. Narrow axial bore 69 through shank 68 provides an air ex` haust passage for air between iianges 82 and 66.

In operation, pressurized air is supplied through passage 7'4 against ange face 67 directed away from piston 80, biasing piston 44 leftwardly to override the compressive force of spring 78. Jaw 18 is thus held in a leftward retracted position. Jaw 20 is adjusted to haifva j specimens thickness from the grip centerline by turning the knob 40. The specimen is placed between the jaws and the pressure is released from chamber 72, allowing spring 78 to move jaw 18 against the specimen under a pressure of some 15 p.s.i., thereby safely securing the specimen between the jaw faces 19,. 21. Oil under high pressure is now admitted to recess 54 through passage 56, forcing pressure piston 80 to the right against pistou 44 and applying-'high clamping force at the jaw faces.

The electromechanical system for controlling a pair of grips 10, 10a, arranged to clamp respectively the top and bottom of a specimen is shown schematically in FIG. 2. Solenoid operated 3-way valves 90, 92 control the application of pressurized air to passages 74, 74a from an air supply (not shown) through conduits 94, 96, 98. Valves 90, 92 are normally open but can be closed to exhaust chambers 72, 72a by closing foot pedal operated switches 100, 102 to actuate solenoids 91, 93. Switches 100 and 102 are series connected so that both must Ibe closed to actuate solenoid 93. Further connected in series with switches 100, 102 is push-button operated relay 104, which controls a third solenoid-operated 3-way valve 106. Valve 106 is normally closed and can be opened by actuating relay 104, and hence solenoid 107, only after both switches and 102 are closed. When valve 106 is opened air is admitted from the supply to hydraulic booster 108 through conduit 110, actuating the `booster and causing oil at high pressure to be supplied to re`cesses`54, 54a

through lconduits 112, 114 and passages 56, 56a. In the embodiment shown the booster is adjustable to provide hydraulic pressure of up to 1900 p.s.i. at pressure pistons 80, 80a, resulting in a clamping force at the jaw faces of some 3000 pounds.

Other embodiments will occur to those skilled in the art and are within the following claims.

We claim:

1. A materials vtesting grip comprising a frame with a pair of spaced frame portions extending generally in one longitudinal direction and a testing ymachine mounting portion extending in the other longitudinal direction, a pair of facing jaws carried respectively by said frame portions, and a pair of jaw actuating pistons carried by one of said frame portions, a first of said jaw actuating pistons being selectively operable to drive the jaw carried by said one of said frame portions toward the other jaw with a first force and the second of said jaw actuating pistons being selectively operable only when said first of said jaw actauting pistons is urging said jaw carried by the same fra-me portion as said second actuating piston to urge the last-mentioned jaw toward said other jaw with a second force greater than said first force.

2. The grip of claim 1 in which said second of said jaw actuating pistons drives the respective jaw by urging said first of said actuating pistons against said jaw.

3. The grip of claim 2 in which said first of said actuating pistons is urged toward the respective jaw by a spring, and away therefrom by fluid pressure, and the second of said actuating pistons is urged against the first actuating piston by fiuid pressure.

4. The grip of claim 3 in which said fluids are respectively a gas and a liquid.

5. The grip of claim 1 wherein said first actuating piston has an elongated shank having a free end and an annular spindle surrounding and spaced from said shank and terminating short of the fr ee end of said shank, said second actuating piston has an axial bore for receiving that part of said shank not surrounded by said spindle, and a spring is disposed between said shank and spindle, said spring having an uncompressed length greater than the length of said spindle, whereby said spring urges said first actuating piston laway from said second actuating piston and toward the respective jaw.

6. The grip of claim 5 wherein said spindle has an annular flange extending radially outwardly, said fiange having la face directed away from said second actuating piston, whereby the application of pressurized Vair to said face overrides said spring and urges said first actuating piston away from said respective jaw and toward said second actuating piston.

7. A materials testing grip comprising a frame with a pair of spaced frame portions extending generally in one longitudinal direction and a testing machine mounting portion extending in the other longitudinal direction,

lfirst and second facing jaws carried respectively by said frame portions,

an adjustment member carried by a first of said frame portions for manually adjusting the first jaw carried by said first frame portion toward and away from the second jaw,

a pair of jaw actuating pistons carried by the second frame portion, a first of said pistons having an elongated shank having a free end, an annular spindle surrounding and spaced from said shank and terminating short of the free end of said shank, and an air exhaust bore, said first piston disposed adjacent the second jaw carried by said second frame portion with the free end of said shank directed away from said second jaw, said spindle having an annular flange providing a face directed away from said free end of said shank, the second of said pistons having an axial bore for receiving the free end of said shank, the diameter of said axial bore being smaller than the inside diameter of said annular spindle,

said second frame portion having an end cap, said second piston being shaped at its end opposite said axial bore to seat in said end cap, and a spring disposed between said shank and spindle, said spring having an uncompressed length greater than the length of said spindle, said spring urging said first piston toward said second jaw and away from said second piston,

said second frame portion having a passage communicat-ing with said flange face for the application of pressurized air to said face to override said spring and urge said first piston away from said second jaw and toward said second piston,

said end cap having a fluid passage for the application of fiuid at a high pressure greater than the pressure exerted by said spring to the end of said second piston adjacent said end cap to urge said second piston toward said first piston.

whereby, when said pressurized air is not applied to said face said first piston drives said second jaw toward said first jaw with the force of said spring, and causes said second piston to seat in said end cap, and when said high fluid pressure is applied through said fluid passage in said end cap said second piston drives said second jaw through said first piston toward said first jaw with a force greater than the force of said spring.

8, Fluid operated grip apparatus comprising a grip having a frame, a pair of clamping jaws supported in said frame for receiving a specimen, at least one Of said jaws being movable between a retracted position and a clamping position in which it bears against the specimen, a low pressure piston, biasing means controlling said low pressure piston to bias said movable jaw against the specimen when said jaw is in its clamping position, and a high pressure piston for the application of high fiuid clamping pressure to said movable jaw to urge said jaw at high pressure against the specimen while said jaw is in its clamping position, said low pressure piston being located between said movable jaw and said high pressure piston.

9. The apparatus of claim 8 wherein a spring is located between said pistons and said apparatus further comprises a passage communicating with a face of said low pressure piston directed away from said high pressure piston, said passage enabling the introduction of pressurized air against said low pressure piston to overcome the force of said spring and bias said movable jaw in its retracted position.

10. Fluid operated grip apparatus comprising a grip' having a frame, a pair of clamping jaws supported in said frame for receiving a specimen, at least one of said jaws being movable bet-ween a retracted position and a clamping position in which it 4bears against the specimen, low pressure means for biasing said movable jaw against the specimen when said jaw is in its clamping position, a fluid passage for the application of high fiuid clamping pressure to said movable jaw to urge said jaw at high pressure against the specimen while said jaw is in its clamping position, said low pressure biasing means having a -first condition in which it is disabled from biasing said movable jaw against the specimen and a second condition in which it biases said movable jaw against said specimen, means to change the condition of said low pres` sure biasing means including a rst switch operatively' arranged for initiating said change, a second switch operatively connected to a source of high fluid pressure for initiating the application of high pressure fiuid through said fluid passage, and control circuitry connected so that said second switch is ineffective until said first switch has initiated said change in condition.

11. The apparatus of claim 10 further comprising a high pressure piston and a low pressure piston located between said movable jaw and said high pressure piston,

said low pressure piston being controlled by said biasinU means to bias said movable jaw in its clamping position.

References Cited UNITED STATES PATENTS F. Arnold 269-23 G. N. Lukas 269-23 A. H. Emery 73-103 i 6 OTHER REFERENCES Twing-Albert Co., Catalog, May 2, 1962, page 101. Research Incorporated, Publication, Jan. 4, 1965, p. 1. Research Incorporated, Publication, Feb. 2, 1965, p. 1. 

7. A MATERIALS TESTING GRIP COMPRISING A FRAME WITH A PAIR OF SPACED FRAME PORTIONS EXTENDING GENERALLY IN ONE LONGITUDINAL DIRECTION AND A TESTING MACHINE MOUNTING PORTION EXTENDING IN THE OTHER LONGITUDINAL DIRECTION, FIRST AND SECOND FACING JAWS CARRIED RESPECTIVELY BY SAID FRAME PORTIONS, AN ADJUSTMENT MEMBER CARRIED BY A FIRST OF SAID FRAME PORTIONS FOR MANUALLY ADJUSTING THE FIRST JAW CARRIED BY SAID FIRST FRAME PORTION TOWARD AND AWAY FROM THE SECOND JAW, A PAIR OF JAW ACTUATING PISTONS CARRIED BY THE SECOND FRAME PORTION, A FIRST OF SAID PISTONS HAVING AN ELONGATED SHANK HAVING A FREE END, AN ANNULAR SPINDLE SURROUNDING AND SPACED FROM SAID SHANK AND TERMINATING SHORT OF THE FREE END OF SAID SHANK, AND AN AIR EXHAUST BORE, SAID FIRST PISTON DISPOSED ADJACENT THE SECOND JAW CARRIED BY SAID SECOND FRAME PORTION WITH THE FREE END OF SAID SHANK DIRECTED AWAY FROM SAID SECOND JAW, SAID SPINDLE HAVING AN ANNULAR FLANGE PROVIDING A FACE DIRECTED AWAY FROM SAID FREE END OF SAID SHANK, THE SECOND OF SAID PISTONS HAVING AN AXIAL BORE FOR RECEIVING THE FREE END OF SAID SHANK, THE DIAMETER OF SAID AXIAL BORE BEING SMALLER THAN THE INSIDE DIAMETER OF SAID ANNULAR SPINDLE, SAID SECOND FRAME PORTION HAVING AN END CAP, SAID SECOND PISTON BEING SHAPED AT ITS END OPPOSITE SAID AXIAL BORE TO SEAT IN SAID END CAP, AND A SPRING DISPOSED BETWEEN SAID SHANK AND SPINDLE, SAID SPRING HAVING AN UNCOMPRESSED LENGTH GREATER THAN THE LENGTH OF SAID SPINDLE, SAID SPRING URGING SAID FIRST PISTON TOWARD SAID SECOND JAW AND AWAY FROM SAID SECOND PISTON, SAID SECOND FRAME PORTION HAVING A PASSAGE COMMUNICATING WITH SAID FLANGE FACE FOR THE APPLICATION OF PRESSURIZED AIR TO SAID FACE TO OVERRIDE SAID SPRING AND URGE SAID FIRST PISTON AWAY FROM SAID SECOND JAW AND TOWARD SAID SECOND PISTON, SAID END CAP HAVING A FLUID PASSAGE FOR THE APPLICATION OF FLUID AT A HIGH PRESSURE GREATER THAN THE PRESSURE EXERTED BY SAID SPRING TO THE END OF SAID SECOND PISTON ADJACENT SAID END CAP TO URGE SAID SECOND PISTON TOWARD SAID FIRST PISTON. WHEREBY, WHEN SAID PRESSURIZED AIR IS NOT APPLIED TO SAID FACE SAID FIRST PISTON DRIVES SAID SECOND JAW TOWARD SAID FIRST JAW WITH THE FORCE OF SAID SPRING, AND CAUSES SAID SECOND PISTON TO SEAT IN SAID END CAP, AND WHEN SAID HIGH FLUID PRESSURE IS APPLIED THROUGH SAID FLUID PASSAGE IN SAID END CAP SAID SECOND PISTON DRIVES SAID SECOND JAW THROUGH SAID FIRST PISTON TOWARD SAID FIRST JAW WITH A FORCE GREATER THAN THE FORCE OF SAID SPRING. 